Journal of Electromagnetic Waves and Applications, 2025 (SCI-Expanded)
To meet the demand for multi-port, miniature antennas for implantable medical devices (IMDs), a novel two-port, multi-input, multi-output (MIMO) antenna design is proposed in this article. Each miniature antenna element, consisting of an efficient spiral radiator fed by a microstrip feed line, operates in the 2.45 GHz (ISM) band. The overall size of the miniaturized two-port MIMO antenna with the superstrate is only 6.22 mm3 (7.168 × 3.472 × 0.25 mm3). The prototype of the antenna, whose numerical analysis was conducted in homogeneous skin tissue and a realistic voxel model, was also fabricated. Subsequently, in vitro tests were performed. According to the measurement results, an isolation of more than 20 dB is observed between the ports. In addition, other critical MIMO antenna parameters, such as the envelope correlation coefficient (ECC), diversity gain (DG), and specific absorption rate (SAR), are also investigated, and all of them are found to be within acceptable values for practical applications. As a result, compared to recently reported implantable MIMO antennas, this antenna, which has a smaller and simpler configuration, is believed to be an essential alternative for compact IMDs.